This invention relates to filter apparatus adapted for use with a basin connected to a crude water intake and having a bottom which is permeable to liquids, lies above a filtrate chamber and supports a filter bed. The apparatus also embodies a raisable and lowerable suction bell which is connected to a suction unit and is transportable horizontally through the basin in a raised position above the filter bed and is lowerable into an operable position in which it back-washes a partial volume of the filter bed by the suction action of the suction unit sucking back or withdrawing the filtrate from the filtrate chamber.
Filter apparatus of this type is disclosed in German Offenlegungsschrift No. 2,455,172. A disadvantage of this type filter apparatus is that the basin must be subdivided into compartments in order to be able to apply the suction bell of the apparatus for back-washing the filter bed. The stationary division walls, which are necessary for this purpose, complicate and increase the cost of construction of the basin considerably. Furthermore, all of these compartments should lie in the same plan so that one and the same suction bell can be used for back-washing all the compartments. Such an arrangement is virtually impracticable, particularly for circular basins, because the only conceivable regular subdivision of a circular basin would be in the form of circular sectors.
In sector-shaped compartments the filter bed would be even more inefficient, particularly in the acute angle. Also, due to the nonuniform suction action in such compartments, they would be cleaned unevenly in the back-washing process. It will thus be seen that filter apparatus adapted for use in a circular basin cannot be equipped with such suction units for back-washing the filter bed, unless suction bells of different shapes are used for compartments of different shapes, which would be unsatisfactory due to economic considerations.
Since stationary division walls heretofore used to subdivide filter apparatus basins can be installed subsequently in already existing basins only at high cost, only new filter apparatus can be provided with a filter bed back-washing suction unit which has advantages over other filter bed cleaning devices.